The present invention relates to refurbishment and repair of gas turbine components and, more particularly, to an apparatus and method utilizing a multi-axis robotic arm welder for refurbishing and repairing gas turbine components.
Nickel-base, cobalt-base, and iron-base superalloys have been used in the hot sections of gas turbine engines due to their ability to withstand high operating temperatures while retaining significant strength at up to 80% of the alloy""s melting temperature. Because these alloys are used to such extremes, they tend to suffer different types of damage in operation such as thermal fatigue, oxidation, corrosion, creep, etc. It is often desirable to repair the components rather than replace them due to economic concerns.
Manual use of arc-welding processes such as TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), and PTA (Plasma Transferred Arc) has been performed in the weld repair of gas turbine components. However, as the performance of gas turbine engines increases, use of highly alloyed (increased gamma) ni-base superalloys (including directionally solidified and single crystal) has been required. This class of alloys has found popular use in large frame size industrial gas turbines. Examples include alloys such as GTD-222, IN-939, IN-738, GTD-111 (EA and DS), Mar-M-247 (DS), CMSX-4(SC), and Rene N5 (SC). These alloys, however, also become less weldable or even nearly impossible to weld manually as they are alloyed to the highest strength levels.
Manual TIG welding can be successful with the use of weld fillers like IN-625 and Hast X in low restraint weld geometries and a highly skilled welder. These weld fillers, however, tend to exhibit poor oxidation and creep resistances at the higher temperatures at which today""s modern industrial gas turbines operate. Moreover, even if manual welding is successful, it is difficult to control a multiple pass, three-dimensional manual weld at the tip of a turbine blade (a typical repair location at the first engine overhaul). These geometrical inconsistencies of a manual weld such as a squealer tip wall thickness lead to increased machining or hand grinding times as well as decreased yield at subsequent inspection operations such as FPI (fluorescent penetrant inspection) and X-Ray.
In an exemplary embodiment of the invention, a gas turbine component refurbishment apparatus includes a robotic arm disposed adjacent the gas turbine component, and a welding torch assembly coupled to an end of the robotic arm. A wire feeder cooperates with the welding torch assembly. A robotic arm controller communicates with the robotic arm and controls a position of the robotic arm relative to the gas turbine component. A vision system is coupled with the robotic arm controller for identifying the gas turbine component, defining a weld path according to the gas turbine component contour, and calculating a trajectory for the robotic arm to follow. The vision system communicates the trajectory to the robotic arm. The welding torch preferably includes an arc length voltage controller, a wire feed guide, and a plasma welding torch. The weld path may be provided with a sine wave with a set wavelength and a set amplitude to reduce heat input and to provide a weld width sufficient for the gas turbine component. The apparatus may further include a water-cooled chill fixture that secures the gas turbine component for welding and effects inter-pass temperature control. The robotic arm is preferably a 6-axis robotic arm.
In another exemplary embodiment of the invention, a method of refurbishing a gas turbine component includes the steps of securing the gas turbine component, identifying the gas turbine component, defining a weld path according to the gas turbine component contour, calculating a trajectory for the robotic arm to follow, and welding with the robotic arm and attached welding torch assembly along the weld path. The method may further include welding with an alloy weld filler wire. After the welding step, the method may include the steps of machining the gas turbine component to final dimensions, vacuum heat treating the gas turbine component, and inspecting the gas turbine component. Prior to the securing step, the method may include the step of heat treating the gas turbine component for welding. In this context, the welding step may be performed at room temperature.